1. Field of the Invention
This invention relates to a focus adjusting apparatus of a photographing instrument such as a camera, and in particular to a focus adjusting apparatus having a power focus function.
2. Description of the Prior Art
An automatic focus adjusting apparatus (hereinafter referred to as the AF apparatus) which automatically effects focusing with respect to an object intended to be photographed has a disadvantage that it cannot execute focusing with respect to an object to be photographed when a plurality of objects to be photographed exist in the same photographing picture plane (such fact will hereinafter be referred to as the concurrence of far focus and near focus) or when distance detection is impossible. That is, during the concurrence of far focus and near focus, when the lens is in focus with respect to any of the objects to be photographed which exist in the photographing picture plane, movement of the lens is locked at that position and therefore, focusing with respect to the object intended to be photographed is not always executed. Thus, it would occur to mind to endow the AF apparatus with the function of driving the lens by a motor while an extraneous operating member such as a push button is being operated, electrically effecting focusing, effecting the detection of the in-focus with respect to the object to be photographed while the photographer is visually recognizing the finder image varied by the focusing, releasing the operation of the above-mentioned operating member when the in-focus with respect to the object intended to be photographed is detected, stopping the driving of the motor at that point of time and manually effecting focusing (hereinafter referred to as the manual focusing function by power focus), and to enable focusing to be executed manually in the case of the concurrence of far focus and near focus or in a case where the contrast of the object to be photographed is so low that malfunctioning is liable to occur during the automatic focus adjustment.
The manual focusing function by power focus can solve the problem of focusing under the concurrence of far focus and near focus, as described above, but the detection of the in-focus must be effected while the photographer himself is visually recognizing the manner of blurring of the finder image, as described above, and this leads to the problem of operability.
For this reason, even when focusing is executed manually the use of the power focus function it would occur to mind to cause the distance detecting function (the in-focus state discriminating function) of the AF apparatus to work to display the in-focus state and thereby facilitate the discriminating of the in-focus state.
On the other hand, when focusing is effected manually by power focus, it is necessary to increase the focusing speed in order to improve the operability and therefore, it is expected to effect the stop-down of the lens at a high speed. However, if the focusing speed is increased, the amount of stop-down of the lens may overrun the position whereat display of the in-focus is effected even if the in-focus state is displayed by the above-described method and at that point of time the operation of the operating member is released to stop the motor.
Even if, for this reason, the technique as known, for example, from U.S. Pat. No. 4,314,750 wherein when a desired exposure condition is obtained while the exposure condition is being varied manually, that is, when in-focus is brought about while the focus adjusting ring of the lens is being manually rotated, a signal is imparted to the photographer's hand by click or brake action to cause the photographer to recognize the in-focus and when the photographer has recognized the in-focus, the rotation of the focus adjusting ring of the lens is stopped is applied to the power focus, the result is nearly equivalent to the function of the ordinary AF apparatus and thus, it has been impossible to solve the problem of malfunctioning under the concurrence of far focus and near focus of the ordinary AF apparatus.